This invention relates to semi-automatic full fell seamers for inseams or outseams, or any other full or half fell seams.
It is common knowledge that a full fell seam is one of the most difficult operations in jeans construction. Typically, this job requires a training curve of nine months to one year to reach peak production. Because it is so difficult to master, turnover in that job is higher than in most others. Fell seaming requires a higher degree of skill and dexterity. The constant finger and wrist motion can be a major cause of carpal tunnel or repetitive motion syndrome, a leading cause of workman's compensation claims. Full fell seams are also a major source of quality problems. "Washouts" occur when the operator has failed to push enough material into the folder during the sewing process. Unfortunately that happens far too frequently.
The felled seam operators are widely known to have one of the most difficult jobs in a jeans factory. Operators are required to perform physically challenging tasks as they guide the material into the folder. This skill requires long training time and can result in quality problems such as raw edges, washouts, twisted legs and wasted material, if not performed correctly. Even after the long and rigorous training cycle, the physical demands on the operators result in one of the highest percentage of workman's compensation claims in clothing factories.
The felled seam is one of the most complex and most physically demanding operations in producing a pair of jeans. Normally, the operator is required to constantly fold and steer material into the folder so that the seam is sewn by both needles. That requires a high degree of skill, and thus a high pay level.
The felled seam operation requires one of the highest skill levels, and also requires one of the longest training times. Typically, that operation can require training times up to one year to become fully productive. The importance of training time for this operation is also increased by the high rate of turnover of fell seam operators. In many plants, fell seam operator turnover is over twice as high as other operations, increasing costs and decreasing outputs.
As the operator sews the felled seam (inside or outside), he/she has a tendency to pull one ply in an attempt to assure that the ends of the panels match. That causes a twisted leg.
In sewing the felled seam, because of operator variations and inefficiency, raw edges can occur. In some cases, both panels are not completely folded in, so that the needles do not sew both pieces of material. The operator catches many of those by manually checking each pair. Raw edges lead to undoing the seam and resewing.
Many times, the operator does not find the problem and pressure from washing causes the seam to come undone, called a washout. The pair cannot be sold.
In many operations, to protect against raw edges and washouts the operator may overcompensate and fold in too much material. That may cause lumps, wrinkles or size variations. Those variations in leg size can vary from operator to operator.
The presser foot is normally controlled by a leaf spring and the feed roller is controlled by a compression spring. When crossing a seam, the thickness of the material can increase fourfold, increasing the pressure respectively. If the seam pressure under the presser foot is too high, the feed roller may be unable to pull the material through, resulting in a bog down. When stuck, the friction of the feed roller and feed dogs can wear through and damage the material.
During the sewing of the fell seam common quality issues are ripples or waves in the leg and the wariness in the material after the seam is sewn. The main reason for this is that the feed roller pressure needs to be set so high in order to limit the amount of bog downs. A secondary reason for the ripples is the variation in pressure on the material between the presser foot and feed dogs. That variation is caused by the small range of the leaf spring.
Ergonomics are important. Under normal conditions, the felled seam operator has constant stress on fingers and wrists from folding the material, as well as the neck and back from leaning forward over the folder during sewing. Repetitious movements are also required to inspect each garment for raw edges.